1. Technical Field of the Invention
This invention relates generally to wireless communications; and more particularly to low power high data rate communications.
2. Description of Related Art
Communication technologies that link electronic devices are well known in the art. Some communication technologies link electronic devices via networks. Examples of such networks include wired computer networks, wireless computer networks, wired telephone networks, wireless telephone networks, and satellite communication networks, among other networks. Within such communication networks, a network infrastructure couples electronic devices to one another.
The need for wireless networking has been addressed by various standards bodies that promulgate interworking standards. One such standards body promulgated the IEEE 802.11 standard that defines a wireless LAN. In a typical 802.11 wireless LAN, a wired backbone couples to one or more wireless access points (WAPs) that wirelessly connect to many computers or other electronic devices that contain wireless interfaces. IEEE 802.11 networks have achieved significant success in servicing wireless communication needs for portable computers, portable data terminals, and other wireless devices that transmit and receive data. However, IEEE 802.11 networks lack high data rate and Quality of Service (QOS) features to support multimedia communications.
Wireless personal area networks “WPAN” enable short-range “ad-hoc” connectivity among portable consumer electronics and communications devices but do not require the infrastructure needed for an 802.11 network. The coverage area for a WPAN is generally within a 10-meter radius. The term “ad-hoc” connectivity refers to both the ability for a device to assume either master or slave functionality and the ease in which devices may join or leave an existing network.
The Bluetooth radio system has emerged as the first technology addressing WPAN applications with its salient features of low power consumption, small package size, and low cost. Raw data rates for Bluetooth devices are limited to 1 Mbps, although the actual throughput is about half of the raw data rate. A Bluetooth communication link supports up to three voice channels with very limited additional bandwidth for bursty data traffic. However, Bluetooth communication links cannot support the data transfer requirements of portable consumer electronics devices that transmit and receive multimedia data, e.g., high quality video applications, audio applications, and multi-megabyte file transfers for music and image files.
To support higher data rates in wireless systems, higher order modulations are often employed, e.g., 8-QAM, 16-QAM, 32-QAM, 64-QAM, 128-QAM, etc. However, higher order modulations are susceptible to fading and interference, particularly at the low transmission powers employed in WPAN applications. Thus, to provide flexibility in operation, multiple constellation sizes are typically supported within wireless systems of this type. Larger constellations are used for higher quality channels while smaller constellations are used for lower quality channels.
Forward Error Correction (FEC) is commonly included in wireless systems. The usually employed Reed Solomon block codes add non-information-carrying parity bytes to the transmitted data bytes. In the absence of errors FEC reduces the actual data throughput for a given channel bit rate. However, when errors occur, the capability of correcting errors up to a certain extent decreases the number of required retransmissions thereby increasing the effective data throughput.
While FEC schemes operate on hard-quantized bits and/or bytes, it is desirable to provide an “inner” coded modulation scheme that is more specifically designed to deal with non-binary modulation symbols and noisy received signals. Trellis Coded Modulation (TCM) is a commonly employed inner coding scheme. Further, because the quality of wireless channels changes over time, it is desirable to vary constellation sizes depending on channel conditions. In a WPAN system, for example, each wireless device must therefore support TCM with a plurality of constellation sizes. In order to minimize complexity, it is desirable to use one common TCM scheme for all constellation sizes. This scheme should provide optimal performance for each constellation, which means that for a given number of code states and a given constellation, no other scheme should exist with better performance than the common scheme. Well known TCM schemes are optimal for all types of Quadrature Amplitude Modulation (QAM), but not simultaneously also for Quadrature Phase Shift Keying (QPSK).